Communication and Homeostasis Flashcards
(162 cards)
0
Q
Define a response
A
A change in behaviour or physiology as a result of a change in the environment.
1
Q
Define negative feedback
A
A process that brings about a reversal of any change in conditions.
It ensures that an optimum steady state can be maintained, as the internal environment is returned to its original set of conditions after any change.
It is essential for homeostasis
2
Q
What is insulin?
A
The hormone, released from the pancreas, that causes blood glucose levels to go down.
3
Q
What is an ectotherm?
A
An organism that relies on external sources of heat to regulate its body temperature.
4
Q
Define homeostasis
A
The maintenance of a constant internal environment, within narrow limits, despite external changes
5
Q
What is multifunction?
A
One presynaptic neurone might diverge to several postsynaptic neurones.
This allows signals to be transmitted to several parts of the nervous system, useful in a reflex arc
6
Q
What is a polarised membrane?
A
A membrane that has a potential difference across it. This is the resting potential.
7
Q
What carries the action potential from a sensory receptor to the central nervous system.
A
Sensory neurone
8
Q
What is depolarisation?
A
The loss of polarisation across the membrane.
It refers to the period when sodium ions are entering the cell making the inside less negative with respect to the outside.
9
Q
Define a stimulus
A
A change in the internal or external environment of an prganisms that causes a response.
10
Q
What carries an action potential from the central nervous system to an effector
A
A motor neurone
11
Q
What is an action potential?
A
It is achieved when the membrane is depolarised to a value of about +40mV.
It is an all-or-nothing response. Only ever goes in one direction.
12
Q
What are hormones?
A
Molecules that are released by endocrine glands directly into the blood.
They act as messengers, carrying a signal from the endocrine gland to a specific target organ or tissue.
13
Q
What is glucagon?
A
The hormone, released from the pancreas, that causes blood glucose levels to rise.
14
Q
What is a neurotransmitter?
A
A chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone.
15
Q
What is the synaptic knob?
A
The swelling at the end of the presynaptic neurone
16
Q
What is saltatory conduction?
A
It refers to the way that the action potential appears to jump from one Node of Ranvier to the next
17
Q
What is an endotherm?
A
An organism that can use internal sources of heat, such as heat generated from metabolism in the liver, to maintain its body temperature
18
Q
What is acetylcholinesterase?
A
An enzyme in the synaptic cleft. It breaks down the transmitter subatance acetylcholine.
19
Q
Define resting potential
A
The potential difference across the neurone cell membrane while the neurone is at rest.
It is about -60mV inside the cell compared with the outside
20
Q
All-or-nothing
A
Refers to the fact that a neurone either conducts an action potential or does not.
All action potentials are of the same magnitude, +40mV.
21
Q
Define summation
A
A term that refers to the way that several small potential changes can combine to produce one larger change in potential difference across the membrane.
22
Q
What are voltage-gated ion channels?
A
Channels in the cell membrane that allow the passage of charged particles or ions.
They have a mechanism called a gate which can open and close the channel. The gates respond to changes in the potential difference across the membrane.
23
Q
A muscle tissue that can initiate its own contractions, e.g. Cardiac muscle
A
Myogenic
24
Synapses ensure that signals are transmitted in the correct direction- only the presynaptic knob contains vesicles of acetylcholine.
Unidirectional
25
What is an endocrine gland?
A gland that secretes hormones directly into the blood. These glands have no ducts.
26
Define memory formation
The creation of specific pathways within the nervous system is thought to be the basis of conscious thought and memory
27
What is an exocrine gland?
A gland that secretes molecules into a duct that carries the molecules to where they are used.
28
What is a target cell?
Cells that possess a specific receptor on their plasma membrane.
The shape of the receptor is complementary to the shape of the hormone molecule.
29
What is adenyl cyclase?
An enzyme associated with the receptor for many hormones, including adrenaline.
It is found on the inside of the cell surface membrane.
30
Define spacial summation
Several presynaptic neurones might converge to one postsynaptic neurone. This allows signals from different parts of the nervous system to create the same response.
31
Define a generator potential
A small depolarisation caused by sodium ions entering the cell.
32
What is a secondary messenger?
A molecule that transmits a signal inside the cell e.g. cAMP
33
Define acclimatisation
After repeated stimulation a synapse may run out of vesicle containing the neurotransmitter.
The synapse is said to be fatigued, hence the nervous system no longer responds to the stimulus.
This is why we can get used to a smell etc.
34
Define temporal summation
A low-level stimulus can generate several successive action potentials in the presynaptic neurone, the release of many vesicles of acetylcholine over a short period of time can combine to produce an action potential.
35
Define positive feedback
A process that increases any change detected by the receptors.
It tends to be harmful and does not lead to homeostasis
36
What are the islets of Langerhans?
Small patches of tissue in the pancreas that have an endocrine function.
They consist of alpha and beta cells
37
Diabetes mellitus
A disease in which blood glucose cannot be controlled effectively.
38
Alpha cells
Secrete the hormone glucagon. Found in the islets of Langerhans.
39
Relay neurone
Connect between sensory and motor neurones
40
What are hepatocytes?
Liver cells. They are specialised to perform a range of metabolic functions.
41
Beta cells
Secrete the hormone insulin. Found in the islets of Langerhans.
42
Hyperglycaemia
The state in which the blood glucose concentration is too high.
43
What is a cholinergic synapse?
A synapse that uses acetylcholine as its transmitter substance.
44
Define habituation
If a low-level stimulus creates an action potential in the presynaptic neurone, it is unlikely to pass across the synapse to the next neurone because several vesicles of acetylcholine must be released to create an action potential in the next neurone.
45
Define hypoglycaemia
The state in which the blood glucose concentration is too low.
46
Type 1 diabetes
Insulin dependant diabetes
47
Define cell metabolism
The result of all the chemical reactions taking place in the cytoplasm.
48
What is the vagus nerve?
A nerve that causes a decrease in heart rate, runs from the medulla oblongata to the heart.
49
What is the cardiovascular centre
A specific region of the medulla oblongata that receives sensory inputs about levels of physical activity, blood carbon dioxide concentration and blood pressure.
It sends nerve impulses to the SAN to alter the frequency of excitation waves.
50
Type 2 diabetes
Insulin independant diabetes
51
What is the pancreatic duct?
A tube that collects all the secretions from the exocrine cells in the pancreas and carries the fluid to the small intestine
52
What is the accelerator nerve?
A nerve that causes an increase in heart rate, runs from the medulla oblongata to the heart.
53
What is the medulla oblongata?
Found at the base of the brain, it is the region of the brain that coordinates the unconscious functions of the body such as breathing rate and heart rate
54
What is the first messenger
The hormone that transmits a signal around the body
55
Define the threshold potential
A potential difference across the membrane of about -50mV.
If the depolarisation of the membrane does not reach this value then no action potential is created.
If this value of is reached, then an action potential is created.
56
What are the advantages endothermy?
– A fairly constant body temp, whatever the temperature is externally
– Activity possible when external temperatures are cool - such as at night, early morning or during winter
– Ability to inhabit colder parts if the planet
57
What are the disadvantages of endothermy?
– A significant part of the energy intake used to maintain body temp in the cold
– More food required
– Less of the energy from food is used for growth, or more food is needed in order to grow
58
What are the advantages of ectothermy?
– Use less food in respiration
– They need to find less food to survive and may be able to survive long periods without eating
– A greater proportion of the energy obtained from food can be used for growth
59
What are the disadvantages of ectothermy?
– Less active in cooler temps, and may need to warm up in the morning before they can be active. This puts them at greater risk of predation
– They may not be capable of activity during winter as the never warm up sufficiently.
This means they must have sufficient stores of energy to survive over winter without eating
60
What are local currents?
The movements of ion along the neurone
The flow of ions is caused by an increase in concentration at one point, which causes diffusion away from the region of higher concentration
61
Define the refractory period
A short time after each action potential, when it is impossible to stimulate the cell membrane to reach another action potential
This allows the cell to recover after each action potential. It also ensures are transmitted in only one direction
62
Define threshold value
The minimum intensity that a stimulus must reach for an action potential to be generated
63
What is a synaptic vesicle?
A vesicle produced in the presynaptic neurone, containing a neurotransmitter
64
What is the synaptic cleft?
A narrow gap between two neurones, at a synapse across which a neurotransmitter can pass
65
What is a synapse?
A junction between two adjacent neurones
66
What is the sympathetic nervous system?
The system that can stimulate effectors, speeding up their activity
67
What is the somatic nervous system?
The system that controls the voluntary (conscious) activity of body muscles
68
What is a neurone?
A specialised nerve cell that conveys information in the form of nerve impulses
69
What is the myelin sheath?
A thick insulating layer around the axon that has high electrical resistance
70
What is a motor neurone?
A neurone that conducts impulses from the CNS to the muscles and glands
71
What is a mechanoreceptor?
A sensory receptor that detects movement, pressure or tension
72
What is iodopsin?
The light-sensitive pigment found in come cell, which absorbs light of high intensities
73
What is a sensory neurone?
A type of neurone that conducts impulses from the receptor organs to the CNS
74
What is a Schwann cells?
A cell wrapped around the axon, forming the myelin sheath
75
What is the postsynaptic neurone?
A neurone that receives a nerve impulse across the synaptic cleft
The neurone contains neurotransmitter receptors in its plasma membrane
76
What is the parasympathetic nervous system?
The system that maintains the normal functioning of the body, helping to keep it in a relaxed unstressed condition
77
What is a rod cell?
A photoreceptor found in the retina that is sensitive to low light intensities
It contains the light sensitive pigment rhodopsin
78
What is the optic nerve?
A cell that transmits nerve impulses from the retina to the CNS
79
What is the pacinian corpuscles?
A pressure receptor located in the skin, joints, tendons. And muscle
80
What is rhodopsin?
The light sensitive pigment found in rod cells, that detects light of low intensities
81
What is the retina?
The photosensitive layer at the back of the eye, which contains rod and cone cells
82
What is a photoreceptor?
A sensory receptor that detects light
83
What is a bipolar cell?
A cell connecting the photosensitive cells in the retina to the ganglion cells
84
What is an axon?
A long single fibre that carries impulses away from the cell body
85
What is bleaching?
The process in which rhodopsin in the rod cells absorbs light and splits into its constituent parst
86
Define the absolute refractory period
The short time (1ms) that follows an action potential when another action potential cannot be created
87
What is the central nervous system?
The system that coordinates the body's responses to stimuli.
This includes the brain and spinal cord
88
What is the autonomic nervous system?
The system that controls the involuntary (subconscious) activities of glands, smooth muscle and cardiac muscle
89
Define an action potential
The temporary reversal of the potential difference across the plasma membrane of an axon when it's stimulated
90
A good cellular communication (cell signalling) system will need to:
— Cover the whole body
— Enable communication both ways
— Be specific
— Rapid
— Differentiate between short term and long term
91
Internal environment of an organism needs to be kept within constant limits of:
— A suitable temperature
— A suitable pH
— An aqueous environment with substrate and products in solution
— Free of toxin and inhibitors
92
The nervous system is structured by:
— Sensory receptors (detects a stimulus)
— Sensory neurone (transmit action potential from sensory receptors to CNS)
—CNS
— Relay neurone (connect sensory neurone to motor neurone)
— Motor neurone (transmit signal from CNS to effector)
93
Sensory receptors are:
Transducers — they convert many forms of energy into electrical impulses (action potentials)
They detect a stimulus by transforming the energy change in the environment to generate an excitatory potential
94
Conditions that must be maintained for homeostasis:
— Core body temperature
— Blood glucose levels
— Blood salt concentration
— Water potential of blood
— Blood pressure
— CO2 concentration
95
Resting potential:
Maintains the inside of the cell more negative to the rest
Polarised membrane at -70mV potential difference
Actively pumps (uses ATP) 3Na+ ions inside per 2K+ ions outside (by Na+ and K+ pumps)
Some K+ ions diffuse back outside (by K+ channel)
Na+ is kept outside (gated Na+ channel is closed)
96
What is the nervous system?
A network of neurones, the brain and the spinal cord that uses electrical impulses (action potentials) to communicate throughout the body
97
Define a chemoreceptor
A sensory receptor that detects chemical stimuli
98
What is an effector?
An organ that produces a change or response when stimulated by a nerve impulse
These organs include muscles and glands
99
What is a ganglion cell?
A cell that connects the bipolar cells in the retina to the optic nerve
100
Define depolarisation
The process in which the inside of an axon starts to become more positively charged relative to the outside
101
What are dendrites!
Highly branched fibres of a neurone that receive nerve impulses
102
What is a Node of Ranvier?
A gap in the myelin sheath where the axon is exposed
103
What is an endocrine gland?
A gland that secretes hormones directly into the blood
Endocrine glands have no ducts
104
What is an exocrine gland?
A gland that secretes molecules into a duct that carries the molecules to where they are used
105
Explain the advantages to the arctic fox having a thicker, white coat in winter
The thicker hair traps more air for insulation to prevent heat loss
The white colour gives it camouflage against the snow so it's prey cannot see it
106
What are the requirements of a good communication system?
To be able to – send messages or signals
– receive messages or signals
– distinguish between different
messages and signals
– extend over the whole body
107
Explain the difference between negative and positive feedback
Negative feedback monitors a change and initiates a response that will reverse the change. It will maintain constant levels
Positive feedback monitors a change and initiates a process that will increase the change. It tends to be destabilising
108
Explain why it is important to maintain a constant body temperature
If temperature is too low, enzyme activity falls and the rate of metabolism drops
High temperatures may denature proteins such as channel proteins in membranes and enzymes
109
Explain how basking on a hot rock in the sun can help an ectotherm to regulate its body temperature
If the ectotherm is too cool it can absorb heat from the rock and directly from the sun.
This will warm its skin and blood flowing through the skin
The extra heat is transported around the body to help warm up the muscles
110
Explain why a shrew has to eat its almost its own body mass each day, but an elephant eats less than one percent of its body mass each day
A shrew is very small and has a large surface area to volume ratio. It loses a lot of heat through its skin. Therefore a lot of food must be used to replace the heat lost
An elephant has a small surface area to volume ratio, and therefore loses a much smaller proportion of its body heat
111
Suggest why the fairy penguin of Australia grows to about 25cm in height while the emperor penguin of Antarctica grows to a metre in height
Australia is warm and the penguins do not need to be large to maintain their body temperature
Antarctica is very cold and larger penguins have a smaller surface-area-to-volume ratio – so they can maintain their body temperature more easily
112
Suggest why penguins huddle together
By huddling together, the penguins provide insulation to prevent heat loss and gain warmth from each other
The huddle has a smaller surface-area-to-volume ratio than a solitary penguin
113
Explain how vasoconstriction can prevent heat loss
Vasoconstriction reduces blood flow through the skin
The blood flows through vessels that are deeper in the body
Heat in the blood is less easily radiated out of the body
114
Suggest why neurones need to contain a large number of mitochondria
Mitochondria produce ATP by aerobic respiration to maintain the resting potential and for exocytosis of neurotransmitter at synapses
115
Why do membranes need special channels for the diffusion of charged ions?
Charged ions cannot dissolve in a phospholipid bilayer membrane like that of the axon
Therefore they cannot diffuse across the membrane
The ions need channel protein to produce a hydrophilic channel for diffusion or facilitated diffusion
116
Explain why a neurone is active while it is said to be resting
While the neurone is resting, the membrane is actively transporting sodium ions out of the cell and potassium ions into the cell
117
Outline the need for communication systems witching multicellular organisms, with reference to the need to respond to changes in the internal and external environment, and coordinate the activities of different organs
Organisms need to respond to external stimuli (temp, O2 concentration, levels of sunlight, etc.)
These may be over time (winter fur to summer fur), or quickly (constriction of pupils)
Internal environments change too (CO2 build up changes the pH of tissue fluid, therefore inhibits enzyme activity)
Multicellular organisms need to coordinate different organs, so this requires a good communication system
118
A good communication system will...
Cover the whole body
Enable cells to communicate with each other
Enable specific communication
Enable rapid communication
Enable short term and long term responses
119
Cells need to communicate with each other by a process called...
Cell signalling
120
Neuronal and hormonal systems are examples of...
Cell signalling
121
Explain the principles of homeostasis in terms of receptors, effectors and homeostasis
At change is detected by receptors, the communication system transmits a message from the from the receptor to the effector and, through negative feedback, the effectors reverse the change
122
Describe the physiological changes that maintain a constant core temperature in ectotherms
The horned lizard expands its rib cage, and the frilled lizard uses its frill to expand its surface area to absorb more heat from the sun
Locusts increase their abdominal breathing movements to increase water loss when it's hot
123
Describe the behavioural responses that maintain a constant core body temperature in ectotherms
Snakes expose their body to the sun so more heat is absorbed
Locusts orientate their body towards the sun to expose a larger surface area, so more heat is absorb. They orientate their body away from the sun so more heat is lost
Lizards hide in burrows to prevent heat absorption by staying out of the sun
124
Describe physiological responses that maintains the constant core temperature of an endotherm
Sweating - evaporation, heat loss
Panting - increases water evaporation from lungs, tongue and moist surfaces, heat loss
Hairs on skin - provide insulation when raised, reducing heat loss. Lie flat, provides little insulation, heat can be more easily lost
Vasoconstriction - reduces blood flow to the skin surface, less heat radiated
Vasodilation - allows more blood to skin surface, more heat can be radiated
Increase in metabolism - more heat generated from exergonic reactions
Decrease in metabolism - less heat generated from exergonic reactions
125
Describe behavioural responses that allow ectotherms to maintain a constant core temperature
Hot - Move into shade, hide in burrow
Orientate body to decrease surface area exposed to sun
Remain inactive and spread limbs out to increase surface
area
Cold - Move into sunlight
Orientate body to increase surface area exposed to sun
Move about to generate heat in muscles
126
Outline how peripheral temperature receptors and the hypothalamus are used in endotherms to maintain core body temperature
Endotherms monitor blood temperature in the hypothalamus. If core temperature drops or rises, it sends signals to the effectors to reverse the changes
Peripheral temperature receptors monitor the extremities. The information is fed to the thermoregulatory centre. If it signals a temperature change to the brain, it can initiate behavioural mechanisms for maintaining body temperature
127
Outline the roles of sensory receptors in mammals in converting different forms of energy into nerve impulses
Light sensitive cells in the retina detect light intensity and range of wavelengths (colour)
Olfactory cells in the nasal cavity detect the presence if volatile chemicals
Taste buds detect the presence of soluble chemicals
Pressure receptors in the skin detect pressure on the skin
Sound receptors in the cochlea detect vibrations in the air
Muscle spindles detect the length of muscle fibres
These are all transducers and convert the stimulus to a nerve impulse
128
Describe the structure and function of a motor neurone
A cell body at the end with a large nucleus and lots of rough ER and Golgi bodies
Many short dendrites that carry impulses to the cell body
A long axon that carries an impulse from the cell body to the effector
129
Describe the structure and function of sensory neurones
Long processes on either side of the cell body
A long dendron carrying nerve impulses from a receptor to the cell body
An axon carrying an impulse from the cell body to the CNS
130
Describe and explain how the resting potential is established and maintained
When not conducting an impulse, the potential difference across the membrane is -60mV.
Sodium-Potassium pumps actively transport 3Na+ ions out for every 2 K+ ions in.
The axon contains organic anions, which the membrane is impermeable to.
Slight loss of K+ ions through the permeable membrane.
Membrane impermeable to Na+ ions.
131
Describe and explain how an action potential is generated.
1. The membrane is at resting state; -60mV inside compared to outside. Polarised.
2. Na+ ion channels open and some Na+ ions diffuse out.
3. The membrane depolarises- it become less negative with respect to the outside and reaches the threshold potential of -50mV.
4. Voltage-gated sodium ion channels open and many Na+ ions enter. As more Na+ ions enter, the more positively changed the cell becomes, compared to outside.
5. The potential difference across the membrane reaches +40mV. The inside is now positive compared to the outside.
6. The Na+ ion channels shut and the K+ ion channels open.
7. K+ ions diffuse out of the cell, bringing the potential difference back to negative compared with the outside- repolarisation.
8. The potential difference overshoots slightly, making the cell hyperpolarised.
9. The original potential difference is restored, so the cell returns to its resting state.
132
Describe and explain how an action potential is transmitted in a myelinated neurone, with reference to the roles of voltage-gated sodium ion and potassium ion channels.
The myelin sheath is an insulating layer of fatty material which Na and K ions cannot pass through.
Between the Schwann cells are gaps - called the Nodes of Ranvier, which contain Voltage-gated Sodium and Potassium ion channels, allowing ionic exchange to occur.
The action potential ‘jumps’ from one node to the next
133
Outline the significance of the frequency of impulse transmission.
A stimulus at the higher intensity will cause the sensory neurons to produce more generator potentials. More frequent action potentials in the sensory neurone
More vesicles released at the synapse
A higher frequency of action potentials in the postsynaptic neurone
A higher frequency of signals to the brain
A more intense stimulus
134
Compare and contrast the structure and function of myelinated and non-myelinated neurones.
Myelinated neurones
100-120ms^-1
Up to 1m transmission distance
Fast response time
Used in movement
1/3 of all neurones
One neurones is surrounded by one Schwann cell,
wrapped round many times
Non-myelinated neurones
2-20ms^-1
mm or cm transmission distance
Slow response time
Used in breathing and digestion
2/3 of all neurones
Many neurones are surrounded by one Schwann cell
135
Describe the structure of a cholinergic synapse.
The synaptic knob contains:
• Many mitochondria
• A large amount of smooth ER
• Vesicles containing acetylcholine
• There are also voltage gated sodium ion channels in
the membrane
The postsynaptic membrane contains:
• Specialised sodium ion channels that will only open
when acetylcholine binds to them
136
Outline the role of neurotransmitters in the transmission of action potentials.
A neurotransmitter is a chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone.
They cause the generation of a new action potential in the postsynaptic neurone.
In cholinergic synapses the neurotransmitter is acetylcholine. It is stored in vesicles in the synaptic knob, and when the action potential arrives, the voltage gated sodium ion channels open, so calcium ions diffuse out.
This causes the vesicles to fuse with the synaptic membrane, so acetylcholine is released by exocytosis.
It diffuses across the cleft and binds to receptor sites on the sodium ion channels on the postsynaptic membrane. Sodium ions diffuse across the synaptic membrane into the postsynaptic neurone, creating a generator potential.
If the generator potential is sufficient, the potential across the membrane reaches the threshold potential, and a new action potential is created.
137
Outline the roles of synapses in the nervous system.
Primarily, the role of synapses is to connect two neurones together to pass a signal from one to the other, but they do have other functions:
• Several presynaptic neurones may converge together
to allow signals from different parts of the nervous
system to create the same response.
• One presynaptic neurone may diverge to several post
synaptic neurones to allow one signal to be
transmitted to several parts of the nervous system-
one may elicit a response, and one may inform the
brain.
• They ensure that signals are transferred in only one
direction- only the presynaptic knob contains
acetylcholine in vesicles.
• They can filter out unwanted low-level signal, possibly
created by a low level stimulus. Several vesicles of
acetylcholine must be released for an action potential
to be created in the post synaptic neurone.
• Low level signals can be amplified by summation
(when several small potential charges combine to
produce one larger charge in the potential membrane).
If a low-level stimulus is persistent, it can generate
several successive action potentials in the presynaptic
neurone. The release of many vesicles of acetylcholine
in a short space of time will enable the postsynaptic
generator potentials to combine together to produce an
action potential.
• Acclimatisation- after repeated stimulation, a synapse
may run out of vesicles containing the transmitter
substance. The synapse is said to be fatigued. This
helps avoid overstimulation of an effector, which could
damage it.
• The creation of specific pathways in the nervous
system is thought to be the basis of conscious thought
and memory.
138
Define the term endocrine gland
A gland that secrets hormones directly into the blood. Endocrine glands have no ducts.
139
Define the term exocrine gland
A gland that secrets molecules directly into a duct that carries the molecules to where they are used.
140
Define the term hormone
A molecule released into the blood which acts as a chemical messenger
141
Define the term target tissue
A group of cells that have receptors embedded in the plasma membrane that are complementary in shape to specific hormone molecules. Only these cells will respond to the specific hormone.
142
Explain the meaning of the terms first messenger and second messenger, with reference to adrenaline and cyclic AMP (cAMP).
The first messenger is the hormone that transmits a message around the body, e.g. adrenaline.
The second messenger, e.g. cAMP transmits a signal inside the cell.
143
Describe the functions of the adrenal glands.
The adrenal glands have two distinct regions - the cortex region and the medulla region. The adrenal medulla releases adrenaline, which:
* Relaxes smooth muscle in the bronchioles
* Increases the stroke volume of the heart
* Increases heart rate
* Causes general vasoconstriction- raising blood pressure
* Stimulates conversion of glycogen to glucose
* Dilates the pupils
* Increases mental awareness
* Inhibits the action of the gut
* Causes body hair to erect
The adrenal cortex releases cholesterol. Cholesterol is used to make steroid hormones in the body;
•Mineralalocorticoids help control the concentrations of Na
and K in the blood
•Glucocorticoids help control the metabolism of
carbohydrates and proteins in the liver
144
Describe the histology of the pancreas, and outline its role as an endocrine and exocrine gland.
The cells surrounding exocrine gland of the pancreas secretes digestive enzymes into the pancreatic duct, which then goes onto the small intestine. This is the majority of the pancreas.
The exocrine cells- the Islets of Langerhans- consist of α and β cells. The α cells manufacture and secrete glucagon, whereas the β cells manufacture and secrete insulin. They are involved in the regulation of blood glucose levels.
145
If blood glucose concentration drops too low:
• Detected by α cells
• The fall inhibits insulin production
• They secrete glucagon into the blood
• Bind to receptors on hepatocytes
o Glycogenolysis- conversion of glycogen to glucose
o More fatty acids are used in respiration
o Gluconesgenesis- conversion of amino acids and fats to
glucose
• More glucose in the bloodstream
146
If blood glucose concentration rises too high:
• Detected by β cells
• The rise inhibits glucagon production
• Secrete insulin into the blood
• Bind to receptors on hepatocytes, in the liver
• This activates adenyl cyclase in the cell
• Converts ATP to cAMP
• The cAMP activates a series of enzyme catalysed reactions within the cell;
o More glucose channels are places in the cell surface
membrane
o More glucose enters the cell
o Glycogenesis- glucose in the cell is converted to
glycogen
o More glucose is converted to fats
o More glucose is used in respiration
147
Outline how insulin secretion is controlled, with reference to potassium channels and calcium channels in beta cells.
1. The cell membranes of the β cells contain Ca2+ and K+ ion channels.
2. The K ion channels are normally open, and the Ca ion channels are normally shut. K ions diffuse out of the cell, making the inside more negative.
3. When glucose concentrations outside of the cells are high, glucose molecules diffuse into the cell.
4. The glucose is quickly metabolised to ATP.
5. The extra ATP causes the K ion channels to close.
6. The K ions can no longer diffuse out, so the cells become less negative inside.
7. This change in potential difference opens the Ca ion channels.
8. Ca2+ ions enter the cell and cause the secretion of insulin by making the vesicles containing insulin move to the cell surface membrane and fuse with it, releasing insulin by exocytosis.
148
Compare and contrast the causes of Type 1 (insulin-dependent) and Type 2 (non-insulin-dependent) diabetes mellitus.
Type I Diabetes
Auto-immune response in which body’s β cells are attacked and so insulin is not produced
Treatment-injections and blood glucose concentrations are closely monitored
Type II Diabetes
Body can produce insulin but insulin receptors lose ability to detect and respond to insulin
Treatment-monitoring and controlling diet and may be supplemented by injections
149
Discuss the use of insulin produced by genetically modified bacteria, and the potential use of stem cells, to treat diabetes mellitus
```
GM bacteria:
• Exact copy of human insulin.
o Faster acting.
o More effective.
• Less chance of developing tolerance.
• Less chance of rejection.
• Cheaper.
• More adaptable to demand.
• Less likely to have moral objections.
```
Stem cells
• Could be used to produce new β cells.
• Scientists have found stem cells in the pancreas of adult mice.
• Undifferentiated.
150
Outline the hormonal and nervous mechanisms involved in the control of heart rate in humans.
Action potentials sent down the Accelerator Nerve to the heart; from the Cardiovascular centre of the medulla oblongata cause the heart to speed up. This may be because of:
• Movement of limbs detected by stretch receptors in
muscles
o Extra oxygen may be needed
• Drop in pH detected by chemoreceptors in the carotid
arteries, the aorta and the brain (when we exercise we
produce CO2, this may react w/ H2O in the blood and
reduce the pH).
o CO2+H2O → H2CO3
o H2CO3 →H+ + HCO3-
Action potentials sent down the Vagus Nerve decreases the heart rate. This may be because of:
• Blood pressure rising
When the concentration of CO2 in the blood falls, it reduces the activity of the Accelerator Nerve, slowing the heart rate.
The presence of Adrenaline increases the heart rate to prepare the body for activity.
151
Which important factors must be kept constant in intercellular fluid?
It must contain the correct quantities of oxygen and nutrients, and have optimum pH, temperature and water potential
152
Name the process by which the liver converts one amino acid into another
Transamination
153
Describe the role of the liver in the metabolism of lipids
Excess fatty acids and glycerol are converted into triglycerides and these are transported to storage sites as lipoproteins
Triglycerides can be hydrolysed by lipase enzymes to release fatty acids and glycerol for respiration
The liver also helps regulate the cholesterol content of the blood
154
Describe the role of the liver in the removal of harmful substances from the body
Alcohol, drugs and other toxins are converted into less harmful compounds by the liver, so they can be excreted from the body
155
Name the roles of the liver in homeostasis
Metabolism of lipids
Removal of harmful substances from the body
Regulation of blood glucose
Production of bile
Synthesis of plasma proteins
156
What process is responsible for the removal of sodium and chloride ions from the ascending limb of the loop of Henle?
Active transport
157
What causes the increase in urea concentration as filtrate passes through the collecting duct?
Water is reabsorbed from the glomerular filtrate as it passes through the nephron, so by the time the filtrate reaches the collecting duct, the concentration of urea is much higher than in the blood plasma
As the filtrate passes down the collecting duct, more water is reabsorbed into the blood, increasing the concentration of urea even further
158
What is thermoregulation?
The process of maintaining a relatively constant body temperature, despite fluctuations in the temperature of the external environment
159
Glucose is reabsorbed in the proximal convoluted tubule. Give two features of the cells lining this tubule that makes them well adapted for reabsorption
The presence if microvilli on the surface of the cells increases the surface area available for reabsorption of glucose
They have many mitochondria, to supply the ATP required for the active transport of glucose
160
Will a longer loop of Henle cause the production of more or less concentrated urine?
More concentrated
161
Why is glucose a vital nutrient for all living things?
It is the main substrate for respiration
